Keyless entry systems for vehicles, for example, automobiles such as cars, trucks, and the like, are known in the art. Conventional keyless entry systems often use some form of electromechanical switch arrangement, for example, an array of membrane switches, as a means for a user to input a number combination. A control circuit detects actuations of the switches. When the control circuit determines that the switches have been actuated in a predetermined sequence, the control circuit provides a signal to a lock controller to lock, unlock, or unlatch an entry point of the vehicle, for example, a door, hatch, or tailgate of the vehicle.
Electromechanical switches have certain shortcomings, especially when used in a vehicular environment. Electromechanical switches include moving internal parts, for example, electrical contacts, that can wear out through repeated use. Also, these internal parts can corrode when exposed to the elements, as one might expect they would be when used in a vehicular environment, thereby adversely affecting their performance. Efforts have been made to encapsulate the internal parts and thereby protect them from the environment, but the encapsulation means themselves can wear out from repeated use, abuse or environmental effects, thereby negating their value in providing protection to the internal parts.
Efforts have been made to substitute discrete capacitive touch sensors for electromechanical switches in keyless entry applications. Such sensors typically include some form of discrete touch sensing electrode, for example, a conductive metal pad, for sensing touch. A control circuit provides an excitation signal to the electrode, establishing a capacitance between the touch sensing electrode and another electrode or ground (or another reference potential). Introduction of a stimulus, for example, a user's finger or other conductive object, proximate the sensing electrode alters this steady-state capacitance. The control circuit detects the capacitance and changes thereto and determines that a touch event has occurred when the capacitance changes by at least a predetermined amount from the steady-state capacitance. When the control circuit determines that the sensors have been actuated in a predetermined sequence, the control circuit provides a signal to a lock controller to lock, unlock, or unlatch an entry point of the vehicle, for example, a door, hatch, or tailgate of the vehicle.
Capacitive touch sensors typically have no moving parts, and they can be more readily protected from the environment than electromechanical switches in keyless entry applications. Nevertheless, the use of capacitive touch sensors in vehicular keyless entry systems has certain shortcomings. For example, it can be difficult to calibrate capacitive touch sensors to reliably respond to touch by both gloved and ungloved hands. Also, capacitive sensors used in vehicular keyless entry systems tend to be placed in locations where they are prone to false actuation due to the effects of contaminants such as water, road salt, dirt, other particulates, and the like. As such, known keyless entry systems using capacitive touch sensors have met with limited success.